Many devices exist for controlling the position of a cursor on a display screen. One of the more widely used is the mouse, but it exhibits two major drawbacks. The first is that the user's hand must be removed from the keyboard to control the movement and position of the mouse. The second is that a flat surface adjacent to the keyboard must be reserved for the mouse. To overcome those problems, a number of alternative mechanisms have been devised. In U.S. Pat. No. 4,313,113 to Thornburg, directional movement keys are incorporated directly into the keyboard. In Japanese Patent 60-235227 to Masuta, a pair of orthogonally oriented rollers are incorporated in the keyboard and by manipulation, enable the movement of a cursor across the display's screen. In the IBM Technical Disclosure Bulletin, Vol. 21, No. 7, pp. 3026 and 3027, a similar arrangement is shown but the rollers are incorporated in a separate, free-standing control unit. In U.S. Pat. No. 4,692,756 to Clark, a moveable sleeve is mounted on the keyboard and is hand operable, both vertically and horizontally, to provide cursor control signals.
Recently, a new mechanism has been developed which provides directional control signals for a cursor, but allows both of the users hands to remain in contact with the keyboard. In U.S. Pat. No. 4,712,101 to Culver, this mechanism is shown as comprising a rotatable shaft on which a hollow cylinder is mounted. Rotation of the cylinder rotates the shaft through frictional engagement. The cylinder is also movable longitudinally along the axis of the shaft. One encoder is coupled to the shaft and provides rotary shaft movement signals and another encoder is coupled to the cylinder via a wire and pulley system to provide signals indicative of the cylinder's longitudinal movements. A modified version of the this cursor control mechanism is disclosed by Culver in U.S. Pat. No. 4,724,715. Here again, longitudinal movements of a cylinder along a shaft are transmitted by a wire and pulley system and the cylinder's rotary motion is determined via a mechanical linkage or a mouse-like structure.
In U.S. Pat. No. 4,799,049, another version of a cylinder-cursor movement device is shown by Avila et al. Avila et al. employ a mouse which is mounted in contact with a cylinder which both rotates and translates to provide cursor-position control signals.
In copending U.S. patent applications Ser. Nos. 07/309,839 to Ramachandran and 07/309,829 to Cloutier et al., both assigned to the same assignee as this application, roller-operated, cursor control mechanisms are described. In both of those mechanisms, the roller is mounted on a splined shaft, so that the roller can both translate along the axis of the shaft, while simultaneously imparting rotary motion thereto.
Each of the above roller or cylinder based cursor-control mechanisms exhibits a weakness in translating the rotational motion of the roller to an encoder. In the aforementioned copending applications, after continuous use, internal wear in the cylinder creates erratic translation of the cylinder's rotary motion to the splined shaft and thence to a rotary encoder. The gearing and cable/pulley systems described in the Culver patent also exhibit similar "hysteresis" problems--especially after wear has occurred in the mechanism. The Avila et al. mechanism requires a relatively constant level of friction between the mouse and the cylinder for there to be consistent output readings. Any contaminants appearing on the cylinder will tend to create an erratic interface between the cylinder and mouse, thereby resulting in potentially erroneous readings.
Accordingly, it is an object of this invention to provide a keyboard-mounted, cursor position controller which exhibits consistent and accurate rotary position outputs.
It is another object of this invention to provide a keyboard mounted, cursor position controller wherein usage wear is minimized.
It is still another object of this invention to provide an improved roller-based, cursor position controller.